1. The Field of the Invention
The present invention relates to methods of manufacturing lime pellets for use in asphalt applications. More particularly, the present invention relates to lime pellet compositions and methods of using lime pellets in asphalt manufacturing and paving.
2. The Related Technology
Asphalt pavements are well-known and have been used for many years. Typically, an asphalt pavement includes an aggregate and asphalt cement mixed together in what is commonly referred to as hot mix asphalt (HMA). The asphalt cement is a hydrocarbon-rich substance such as, or prepared from, bitumen, and is used to bind the aggregate into a pavement. The type and amount of aggregate can vary, and it provides structural reinforcement and durability to the HMA. While the asphalt cement functions as a continuous phase that binds the aggregate materials together, it is well known that various additives such as lime can be used to improve the durability and longevity of asphalt pavements.
Traditionally, lime fines have been used in treating HMA ingredients in order to improve the long-term interactions or bonds between the asphalt cement and aggregate. Such improvements have included anti-strip characteristics and reduced deformation or softening of the asphalt pavement over time. These improvements have been obtained by either combining the lime fines with the aggregate or with the asphalt cement before the aggregate and asphalt cement have been prepared into hot mix asphalt. It is thought, without being bound thereto, that lime improves the physical characteristics of the asphalt pavement by inhibiting any absorbed water from softening the pavement, and/or by enhancing the physical interface and bonding between the aggregates and the asphalt cement.
Typically, the lime fines have been added in bulk to one of the hot mix asphalt ingredients by well-known methodologies and techniques. More particularly, the powdered lime can be supplied by inline injection, or bulk dumping. While favorable asphalt pavement characteristics can be obtained by the current methodologies, problems have arisen from the lime fines clumping or becoming airborne, which jeopardizes the ability to accurately measure or control the amount of lime being used.
Additionally, lime fines have been identified as a health hazard because the particulates are easily airborne and can be breathed into a person's lungs. People working directly with the lime mixing process, as well as those in surrounding areas, have been exposed to the airborne lime fines that travel throughout a processing or construction site. In part, this is because the lime fines can become airborne during transportation, loading, unloading, and while being used in the manufacturing process. When lime fines are breathed into the lungs, oxygen is depleted so as to cause suffocation or asphyxiation. While actual death may not be a common result of such suffocation, constant or repeated inhalation of particulate materials can have serious negative long-term implications such as emphysema, pneumonia, chronic bronchitis, and even lung cancer.
Moreover, the use of lime fines to marinate the aggregate has also caused other health-related complications. This is because the powdered lime fines are usually combined with the aggregate and allowed to sit on the ground for weeks or months. As a result, the lime fines have leached into the groundwater and flowed into neighboring aquifers. The presence of lime fines in the water kills fish, and can contaminate drinking water.
Furthermore, the use of lime fines has caused problems with manufacturing and construction equipment. Again, this is at least partially a consequence of the small particulate nature of such lime fines (e.g., smaller than 200 mesh), which allows clouds of the particulates to float or circulate around construction sites and asphalt manufacturing facilities. The small particulates eventually deposit on the machinery or equipment and become entrained within joints and other moving parts. The particles cause excessive wear and fatigue, and result in the equipment wearing out prematurely. Specifically, problems have arisen from the lime fines being sucked into the bags of baghouses so as to foul the bags and render them unusable.
Therefore, it would be advantageous to have a lime product that can be used during the manufacture of HMA and pavement that is not a fine powder. Additionally, it would be beneficial to have a method of processing lime fines into a more manageable form so as to improve their use in asphalt manufacturing and paving with minimal health and cost concerns associated with such small particulates.